Good price, trusted, reliable & very communicative

All in all I'd rate ★★★★☆.

+ price
+ communication (quick answers on whatsapp & facebook; good Englsh)
+ relatively fast (usually less than 48 hours)
+ offered a refund
+ some bonus gems
+ clear processing instructions

- because of a problem the order was delayed by ~12 hours (2.5 days in total)
- only 500 and 1000 gems, no other offers like 250 gems etc.

5th star, if more offers & a little bit faster
Also, next time I'll try negotiating if I can find a cheaper/the same price since he offers to lower the price in that case.
Then it'd be ★★★★★+